Universität Stuttgart
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Item Open Access Computer simulation: splitting tests of concrete thick-walled rings(1992) Pukl, Radomir; Schlottke, Bernd; Ozbolt, Josko; Eligehausen, RolfTwo non-linear program systems are used for a computer simulation of splitting failure of thick-walled concrete rings under internal radial pressure. Results of the numerical analyses for plane stress models, axisymmetrical model and 3D model are compared with available experimental data and empirical formulas. It is shown, that the behavior observed in experiments can be simulated, using advanced material models, namely the non local microplane model and SBETA material model based on the crack hand theory. With increasing outer radius of the ring, a size effect can be observed.Item Open Access Numerical analysis of headed studs embedded in large plain concrete blocks(1990) Ozbolt, Josko; Eligehausen, RolfAnchoring elements such as headed studs, expansion, grouted or undercut anchors are used for local transfer of loads into concrete members. Parameter study of the behavior of headed stud anchors with embedment depth h v= 130 mm and failing by pulling out a concrete cone, is performed through numerical analysis. Compression and tension strength, fracture energy and the head diameter are varied. Numerical analysis is performed using nonlocal microplane model and axisymmetric finite elements. Results of the analysis are compared with experimental results.Item Open Access Fastening elements in concrete structures - numerical simulations(1993) Ozbolt, Josko; Eligehausen, RolfAnchoring elements such as headed and expansion studs and grouted or undercut anchors, are often used for local transfer of loads into concrete members. In order to better understand the failure mechanism, a large number of experiments have been carried out in the past. However, due to the complicated three-dimensional load transfer a very few or no numerical studies have been performed for a number of different fastening situations i.e. influence of the embedment depth, crack-width inftuence (fastening in cracked concrete), influence of the edge distance etc. Therefore, in the present study some results of the axisymmetric and three-dimensional numerical analysis of the headed studs embedded in plane concrete block are presented. Influence of different geometrical and material parameters have been studied employing finite element method and nonlocal microplane model. Comparison between experimental and numerical results indicate reasonable good agreement. Generally it has been observed that the failure mechanism is governed by fracture energy rather than by tensile strength of concrete. As a consequence, the size effect is strong and close to linear elastic fracture mechanics.Item Open Access Simulation of cycling bond-slip behavior(1992) Ozbolt, Josko; Eligehausen, RolfIn the present paper results of a numerical analysis for a deformed steel bar embedded in a concrete cylinder and pulled out by monotonic and cyclic loading are shown and discussed. The analysis is performed by the use of axisymmetric finite elements and an improved 3D general microplane model for concrete, instead of the classical interface element approach, a more general approach with spatial discretization modeling the ribs of a deformed steel bar is employed. The pull-out failure mechanism is analyzed. Comparison between numerical results and test results indicate good agreement. The present approach is able to correctly predict the monotonic as well as cyclic behavior including friction and degradation of pull-out resistance due to the previous damage.Item Open Access Influence of crack width on the concrete cone failure load(1992) Ozbolt, Josko; Eligehausen, RolfIn the present paper the influence of the crack width on the concrete cone failure load of headed anchors embedded in concrete is analyzed. The analysis is carried out on a reinforced concrete thick plate specimen using three-dimensional finite elements and the non local microplane model. In order to introduce precracking into the specimen before loading the headed anchor, the specimen is loaded in longitudinal direction by applying tension forces through reinforcement. At different crack levels pull-out of the fastening element is performed. Results of the analysis show that the concrete cone failure load is decreasing with increasing crack width up to ω ~ 0.15 mm to approximately 70 % of the failure load obtained for non-cracked concrete. Further increase of the crack width does not cause further decrease of the failure load. Comparison between numerical and experimental results indicates good agreement.Item Open Access Analysis of reinforced concrete beams without shear reinforcement using non-local microplane model(1991) Ozbolt, Josko; Eligehausen, RolfThe shear resistance of reinforced concrete beams without shear reinforcement is studied using the non-local microplane model and plane stress finite elements. The main objective of the present work is the study of the size effect. Calculated failure loads for geometrically similar specimens of four different sizes are compared with test data and the recently proposed size effect law. Results of the analysis as well as test results exhibit significant size effect. Observed failure is of the brittle type and is due to failure in tension-compression. Further studies with variations of the mesh size and load path demonstrated that results of the calculations using a non-local continuum are not influenced by the above parameters. However, the calculated failure loads depend on the characteristic length over which the strains are measured. In contrast to that, the calculated failure loads are inobjective when a local continuum is used and depend on mesh size, load path and convergence criteria. This is due to the stability of the numerical analysis, which may lead to an overriding of the critical failure mode and activating to a more stable one. In order to correctly predict failure load using local analysis and crack band approach it is necessary to check the stability of the numerical procedure.Item Open Access Nonlocal fracture analysis - identification of material model parameters(1994) Ozbolt, Josko; Petrangeli, Mario; Eligehausen, RolfIn the present paper a short description of the nonlocal microcrack interaction approach is presented. The physical meaning of this approach when used in the smeared finite element code is discussed. The present nonlocal "averaging" consists of a long-range interaction (crack interaction function) and local averaging. The first controls the crack propagation and the second is responsible for the correct energy consumption due to cracking. It is demonstrated that the nonlocal material model parameters may be identified by usual concrete fracture properties such as tensile strength, concrete fracture energy and maximum aggregate size. The nonlocal microcrack interaction approach is compared with the nonlocal strain approach and a possible simplification is considered.Item Open Access Nonlinear analysis of strain-softening damage under monotonic and cyclic loading(1992) Bazant, Zdenek P.; Ozbolt, Josko; Eligehausen, RolfThe paper reviews the modeling of damage by the microplane model and presents extensions required for cyclic loading. The general microplane constitutive model is implemented in a three-dimensional finite element code and used in damage and bifurcation analysis of various structures. The results of the analysis are compared with test results and some of the comparisons are shown in the present paper.Item Open Access Scaling laws in concrete structures(1994) Ozbolt, Josko; Eligehausen, RolfThere are many experimental evidence on the existence of size effect in concrete structures. The problem has two aspects - statistical and deterministic. Although the statistical aspects are not negligible, in the present paper it is demonstrated that the scaling law is controlled by the structural energy release due to cracking. If a stable crack growth before reaching peak load is possible strong size effect may be expected. For infinitely large structures of these type scaling law based on the linear elastic fracture mechanics must be used. On the contrary, concrete structures fail at crack initiation without any size effect i.e. scaling law based on the strength criteria apply. Due to the finite size of the concrete fracture process zone, size effect for any small structure must exist. Recent numerical investigations using sophisticated numerical tools show that there are many practical examples which exhibit extensive cracking in smaller size range and almost no cracking in larger size range i.e. by increasing size failure mechanism is changing. Practical implication of this is that the size effect may disappear in the case of many large concrete structures. Although this has a strong mechanical background it can also be interpreted from the multifractal damage point of view.Item Open Access Numerical simulation of cyclic bond-slip behavior(1992) Ozbolt, Josko; Eligehausen, RolfIn the present paper the pull-out of deformed steel bar embedded in a concrete cylinder and pulled out by monotonic and cyclic loading is analyzed and discussed. The analysis is carried out by the use of axisymmetric finite elements and general microplane model for concrete. Current version of the model was not able to predict damage in shear due to cycling loading correctly. Therefore, the model is further improved and extended in a more general form. In the present numerical case study, instead of the classical interface element approach, a more general approach is used in which the geometry of the ribs of the deformed steel bar are exactly modeled. In the present numerical case study, the pull-out failure mechanism is analyzed and compared with experimental observations. The comparison indicate qualitatively good agreement. Predicted failure load is in good agreement with experimental results, however, calculated displacement are much smaller than measured in tests . The present approach is able to correctly predict the monotonic as well as cyclic behavior including friction and degradation of pull-out resistance caused by previous damage.